The blog post by Greg Nottage, a consultant with the Windows and Devices Team in the United Kingdom, was a little more definitive than past Microsoft communications in explaining why the LTSC model could be problematic for organizations. Nottage said he specifically works with customers transitioning to Windows 10 and considering using the LTSC update model.

LTSC is similar to Microsoft's update model for Windows 7, with major operating system feature updates arriving perhaps every two to three years. It has a five-year "mainstream support" phase followed by a five-year "extended support" phase, so it's what organizations are used to, and it's what they typically want. Microsoft, though, recommends that organizations use the "semiannual channel" (SAC) model of Windows 10 instead.

The LTSC model is just recommended by Microsoft for use with things like medical devices that can't tolerate frequent changes. It's just for devices using embedded OSes. Nottage said that "LTSC 2016 shares the same codebase as Windows 10 IoT, which is the evolution of Windows Embedded OS."

With the SAC model, major OS feature updates arrive twice per year (in the spring and fall). The updates are referred to as channels, and each channel is supported for 18 months max. The SAC model doesn't have mainstream and extended support phases because new feature updates arrive continuously. They get streamed from Microsoft's content network locations as in-place upgrades, In contrast, IT pros have to install .MSI files to get new OS features under the LTSC model.

Nottage listed 14 reasons why using the LTSC model would be a bad approach for organizations to use. A few of those points stood out, namely:

LTSC does not keep pace with new silicon releases in the same way SAC does -- so LTSC 2016 does not support Intel chips beyond the "Kaby Lake" generation.

No support for Surface hardware.

LTSC does not support ConfigMgr Express Updates.

In-place upgrade from Windows 7 to Windows 10 is not supported for LTSC.

Potential independent hardware and software vendor support and limitations on LTSC.

Non-security operating system fixes and enhancements may not get back-ported to LTSC.

While it's possible Microsoft had communicated these details in its rather extensive Windows-as-a-service documentation, overall, these points seem to be new explanations about why LTSC shouldn't be used by organizations.

In general, Microsoft has also been saying that LTSC isn't for organizations wanting to use it with Microsoft Office or Office 365 ProPlus productivity suites.

Hardware Support
With regard to bullet point No. 1 above about Windows 10 LTSC not keeping pace with silicon, Microsoft's 2016 discussions about silicon support previously had been confined to Windows 7/8.1 on Intel "Skylake" processors, in which support was initially truncated but later reinstated. Back then, Shad Larsen, director of Windows business planning at Microsoft, had assured that "future silicon platforms including Intel's upcoming 7th Gen Intel Core (Kaby Lake) processor family and AMD's 7th generation processors (e.g. Bristol Ridge) will only be supported on Windows 10, and all future silicon releases will require the latest release of Windows 10."

The actual policy is hard to pin down. Microsoft's "Windows Silicon Policy" is listed in this support document. It simply explains that "Windows products will be supported for security, reliability, and compatibility on the latest silicon available at the time of release," without much elaboration.

Gartner's Feb. 2017 report, "Rethink Windows 10 Long Term Servicing Branch Deployment Based on Microsoft's Updated Guidance" (available here), as cited by Nottage, shows a chart on page 3 suggesting that organizations using LTSC could find themselves having to upgrade more frequently because of Microsoft's hardware support stipulations.

Gartner's report also mentioned that Microsoft Surface devices don't support LTSC. The report predicted that "by 2020, LTSB will be used on less than 5% of enterprise PCs."

Other LTSC Limitations
Windows 10 LTSC doesn't support using Express Updates with System Center Configuration Manager, which seems to be new information. Express Updates contain just the changes between the current month's cumulative update and the prior month's cumulative update, according to this Microsoft document. Apparently, LTSC users just get security-only updates each month.

Nottage's list also indicated that nonsecurity Windows 10 "fixes and enhancements may not get back-ported to LTSC." Presumably, he's referring not to new features, but to fixes for existing OS features. It's unclear why such fixes may not arrive.

Lastly, LTSC isn't a choice when using Windows Defender Advanced Threat Protection service, it seems, because it "does not keep pace with feature enhancements." Here, Microsoft is being more specific than in prior announcements. In the past, Microsoft had just generally indicated that LTSC might not support Microsoft's security advances.

Windows Update for Business
In other deployment news, Microsoft last week promised that Windows Update for Business will be getting greater controls over Windows 10 updates. Updates can be paused and uninstalled now, according to an announcement. It's possible to roll back an update if using Microsoft Intune with Windows Update for Business.

The announcement also suggested that it will be possible for Windows Update for Business users to specify when SAC and SAC-T (targeted) releases should get installed. While such a capability seems overdue, Microsoft recently suggested it'll be dropping the SAC-T designation soon. It's a point that will require some further clarification to figure out what Microsoft is trying to do.

Also last week, Microsoft announced that the latest Microsoft Assessment and Planning Toolkit version 9.9 has been released. It's used to assess migration projects, with support for Windows 10, Windows Server 2016 and SQL Server 2017.